STiC — An ASIC CHIP for Silicon-photomultiplier fast timing discrimination

STiC-Silicon Photomultipler (SiPM) Timing Chip, is a prtotype ASIC with 4 channels dedicated to fast timing discrimination in Positron Emmission Tomography using SiPM. It is designed in AMS 0.35μm CMOS technology. Each single channel of the chip can be operated either in constant fraction (CF) or leading edge (LE) triggering mode. The basic principle of the SiPM readout is to sink the current signal into a low impedance current buffer and duplicate the current into two processing paths for later current discrimination. One of the two paths is used for low threshold triggering, which can be applied as LE triggering as well as a Time over Threshold (ToT, with a roughly higher threshold) for energy measurement. The other path passes the signal into a current high pass filter to generate the bipolar pulse for CF timing. Since the input stage of the filter is implemented by an integral capacitor. Measuring the voltage at this point also gives charge of the signal. The engery resoltion of charge measurement is 11% for a ²²Na source. Meawhile 20% resolution is also accomplished using ToT methode. The coincidence timing is 479ps and 712ps (FWHM) repectively for LE and CF. The results of both timing methods are compared and discussed.